SynopsisNylon 6 can exist in either of two stable crystal structures, the a crystal with hydrogen bonds between antiparallel chains or the y crystal with hydrogen bonds between parallel chains. Both structures have been observed in the same highly annealed fiber, suggesting that the polymer should not he regarded as a pure compound hut a multicomponent mixture. Nylon 6 can also exist in a series of metastahle crystal structures which vary continuously in size, perfection, and structural parameters from a pseudohexagonal structure to either of the two stable forms. A single equatorial reflection in the wide-angle x-ray pattern (i.e., pseudohexagonal structure) will not distinguish which of the two stable forms will result upon annealing. Measurement of the 0,14,0 reflection in oriented fibers will distinguish the major trend, but it is still uncertain to what extent annealing conditions can favor one stahle form over the other. The variation in the unit cell parameters as a function of annealing has been accurately measured, and the observed phenomena can he qualitatively described by postulating various balances between the basic forces which hold the crystal together (i.e., hydrogen bonding, dipole-dipole interaction, van der Waals attraction, and covalent bonding).
Historically, DNA has been the target for many metal-based anti-cancer drugs, but drawbacks of prevailing therapies have stimulated the search for new molecular targets which may present unique opportunities for therapeutic exploitation. Enzyme inhibition has recently been identified as an alternative and significant target. The pursuit of novel metallodrug candidates that selectively target enzymes is now the subject of intense investigation in medicinal bioinorganic chemistry and chemical biology. In the field of drug design, it is recognised by many that exploiting the structural and chemical diversity of metal ions for the identification of potential hit and lead candidates can dramatically increase the number of possible drug candidates that may be added to the already abundant armoury of chemotherapeutic agents. This review will focus on recent key advancements in enzyme inhibition as a key target for the development of novel metal-based anti-cancer therapeutics. The enormous clinical success of classical platinum drugs, amongst others, coupled with the wealth of knowledge accumulated in recent years on enzyme structure and function, has undoubtedly been the impetus behind the development of new metallodrug candidates with enzyme inhibitory properties. Recent trends in this field will be reviewed with a particular emphasis on metal complexes that inhibit protein and lipid kinases, matrix metalloproteases, telomerases, topoisomerases, glutathione-S-transferases, and histone deacetylases.
Platinum drugs as anti-cancer therapeutics are held in extremely high regard. Despite their success, there are drawbacks associated with their use; their dose-limiting toxicity, their limited activity against an array of common cancers and patient resistance to Pt-based therapeutic regimes. Current investigations in medicinal inorganic chemistry strive to offset these shortcomings through selective targeting of Pt drugs and/or the development of Pt drugs with new or multiple modes of action. A comprehensive overview showcasing how liposomes, nanocapsules, polymers, dendrimers, nanoparticles and nanotubes may be employed as vehicles to selectively deliver cytotoxic Pt payloads to tumour cells is provided.
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